1. Field of the Invention
The present invention generally relates to gas separation processes and analytical chemical testing equipment. More specifically, the invention is directed to devices and methods for adsorbing the hydrogen sulfide component of the calibration gases that would otherwise be released into the surrounding atmosphere during the calibration of portable gas detectors.
2. Description of the Related Art
Gas detectors and monitors are commonly used in a wide assortment of industrial applications. For example, they are used in the oil and gas industry, power plants, chemical plants, pig farms, grain elevators, sewer plants, landfills and many more places. In these industrial applications, gas detectors and monitors are generally used to monitor and detect the presence of hazardous and explosive gases and oxygen levels in the work environment.
Such gas detectors and monitors usually utilize a number of various types of sensors that are designed to detect and respond to specific, being-tested-for or targeted gases. This use of multiple sensors results in most of these detectors being able to monitor for any one of a number of common gases, the most common of which are oxygen, carbon monoxide, hydrogen sulfide and methane (i.e., the lower explosive limit (LEL) of methane). Single sensor monitors are typically used when there is the potential for exposure to a single gas. The sensors of most gas detectors require a test (i.e., a “bump” test) to confirm that the sensor or sensors are working properly before each use of the detector. Additionally, these sensors also need to be calibrated on a regular basis to make sure their output signals are within an expected or predicted range to known concentrations of the calibration gas. In both types of testing, the test or calibration gases are passed over the sensors and are eventually released into the surrounding or ambient environment. Typical calibration gases include among others: toxic hydrogen sulfide, H2S, at 25 ppm or lower, non-toxic methane, CH4, at 50% LEL (lower explosive limit) which is 2.5% (25,000 ppm) by volume methane, oxygen, O2, concentration ranges from 12% to 18%, and toxic carbon monoxide, CO, at either 50 ppm or 100 ppm. These gases have a balance of air or nitrogen.
When the calibration gas being used is toxic, those who perform such “bump” and calibration tests have reported problems due to the levels of the toxic gases that are released into the surrounding or ambient environment during such tests when they cannot be performed in a ventilated area. Exposure problems when the calibration gas is hydrogen sulfide are often of specific concern.
Hydrogen sulfide is a known highly toxic and flammable gas that is heavier than air and often initially recognized as having a very pungent, rotten-egg-like smell at concentrations as low as 0.005 ppm. It is considered a broad-spectrum poison because it can poison several different systems in the body, although the nervous system is most affected. Its OSHA time-weighted, average exposure limit (TWA, an 8 hour time-weighted average) is 10 ppm. Short-term, exposure to low concentrations can result in eye irritation, a sore throat and cough, nausea, shortness of breath, and fluid in the lungs. Longer-term exposure to such concentrations may result in fatigue, loss of appetite, headaches, irritability, poor memory, and dizziness. Short-term, high-level exposure (i.e., >500 ppm) can induce immediate collapse, with loss of breathing and a high probability of death.
To avoid hydrogen sulfide exposure problems, what is needed is a better way to minimize the amount of this highly toxic gas that is released into the surrounding environment during such gas detector testing procedures.
A quick survey of the patent literature in this area reveals many processes for removing hydrogen sulfide from a gas stream. See, for example, U.S. Pat. Nos. 3,974,256, 4,002,720, 4,061,476, 4,983,365, 5,125,935, 5,177,050, 5,360,468, 5,407,466, 6,284,545, 6,404,205, 6,740,141, 6,858,192, 6,863,713, 7,014,689, 7,101,417, 7,241,430, 7,651,597, 7,704,380, 8,551,229, and 8,646,341. However, none of these are readily applicable for dealing with the small quantities of calibration gases that are utilized in the various gas detector, testing procedures. Thus, there is a continued need for new devices and new methods that can better and is more efficiently remove the hydrogen sulfide component of a calibration gas that would otherwise be released into the surrounding environment during the testing of gas detectors.